The present invention relates to brake actuators for transit-type railway vehicles and in particular to such brake actuators having a spring-applied, air-released auxiliary brake that can be utilized as a parking brake or as an emergency brake in conjunction with the service brake.
Spring-applied, air-released auxiliary brakes are automatically actuated with spring force when air pressure normally holding the spring in a retracted condition is accidentally released. In the case of a loss of braking pressure, due to a broken pipe, for example, the spring force is immediately available to effect a brake application, thereby providing a fail-safe emergency brake. In addition, when the brake pressure is purposely released, such as when draining the system to perform service or maintenance, for example, the spring brake is automatically actuated to provide a parking brake.
It has been long recognized, however, that once the air pressure is released, either purposely or by accident, the spring brake will remain applied until such time as air pressure is restored or the spring is retracted manually. It will be appreciated, therefore, that a manual release arrangement is necessitated with spring-applied, air-released auxiliary brake actuators to permit movement of a railway car that is otherwise rendered inoperative by the absence of air to release the spring-applied, air-released brake. A requirement of these manual release arrangements is that they be automatically reset when the supply of air is restored to retract the spring brake thereby assuring the integrity of the spring brake.